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Mass extinctions: The microbes strike back

By Peter Ward

AROUND 251 million years ago, in the blink of a geological eye, up to 95 per cent of marine species and 85 per cent of those on land went extinct. It was the greatest mass extinction the world has ever endured, and it marked the end of the Permian period. Life took 10 million years to recover.

This cataclysmic event is often portrayed as the time when “life nearly died”, but that is hardly fair. The oldest and most successful life forms on Earth – the bacteria and archaea – sailed through virtually unharmed. The Permian extinction is better seen as a time where life almost went back to normal – when biological conditions that had prevailed on Earth for more than 3 billion years briefly re-established themselves. The microbes did not merely survive; it now appears that they played a leading role in the extinctions.

This new view of the Permian comes not from studying fossilised bones, teeth and shells, but from biochemicals that have been trapped inside rocks for billions of years. This emerging branch of science is called biomarker analysis, or chemical palaeontology, and it is now so powerful that it threatens to make classical palaeontology obsolete. It provides nothing less than a brand new perspective on the history of life on Earth. We now know exactly when the first multicellular organisms evolved, and have made startling insights into the mass extinctions that came to plague them.

Biomarker research has its roots in oil exploration. While palaeontologists dedicated themselves to discovering and describing extinct organisms, geologists were breaking down sedimentary rocks and searching for organic molecules that …